This invention relates to an arithmetic unit for both multiplication and addition.
It has been the practice on calculating a sum of a product and an addend to successively carry out two processes of multiplication and addition. More particularly, a multiplier or multiplication circuit is used at first to carry out a multiplication process of calculating a result of multiplication. In the manner which will later be described more in detail, the multiplication circuit may comprise a partial product circuit for calculating a plurality of partial products in response to a multiplicand and a multiplier which are memorized in two registers, respectively. A Wallace tree, known in the art, may be used in producing a plurality of tree outputs in response to the partial products. Under the circumstances, an adder or totalizer is used to sum up the tree outputs into the result of multiplication which may be called a total product in discrimination from the partial products. After the total product is obtained in this manner, an adder is used in carrying out an addition process of adding the addend to the total product.
A time interval, equal to an interval for the multiplication process plus another interval for the addition process, has therefore been indispensable to get the sum of the total product and the addend. In other words, it has been impossible to get the sum in a short period of time.